The ability to disconnect a teed circuit is currently limited to a ground-mounted solution, e.g. Switching Station. For what is a limited functionality this becomes expensive and time-consuming, and it can be challenging to gain consent to construct a building in a remote position. The proposed solution is to explore the feasibility of an overhead line (OHL) switching solution that can be applied to teed circuits to support the ambitions of SSEN-T to provide quick, efficient connections to deliver earlier and better manage key resources and supply chain.
Benefits
Successful development and rollout of PMS could lead to not only clear financial savings but also an estimated reduction in programme of roughly 2 years due to no buildings being required and a reduction in civil works in comparison to the current switching station solution. Note the overall connection programme will include the associated developer end and connection substation. There will also be a move from Substation and Protection and Control (PnC) resources to build the switching station to OHL and PnC for the PMS. It is anticipated that there will be a significant reduction in overall manhours.
The following benefits could also be realised as a result of this project:
Cost: A reduction in cost is largely attributed to the removal of the switching station with an overhead line-based solution including switchgear being installed on an overhead line structure, no building requirements, and fewer tower modifications. Currently, ahead of further feasibility work, these estimates are based on success in identifying a viable solution that overcomes the current flagged uncertainties.
Programme: A further benefit to PMS is the reduction in the construction programme. A full switching station could take 3 – 4 years to design, consent, and construct compared with approximately 1 – 2 years for the design, section 37 consent, and construction of a PMS solution.
Outages/Maintenance: At this moment in time, maintenance of the proposed switchgear will be reviewed as part of the feasibility study. However, it is anticipated that this would not be more than that required for ground mounted. There would be a need for the maintenance resource to be moved from ground-mounted substation teams to OHL teams and an element of training and tooling/ equipment considered.
Contractor Resource: The work involved in constructing the Pole Mounted Switch solution will be much less than the switching station. The erection of the OHL structures is low-risk and current OHL Contractors will be competent to install. The innovation is around the design and installation of the 4-member structure and forms the main element of the innovation development. However, it is anticipated the design will be aligned with current construction practice. The design, installation, operation, and maintenance of the switchgear will be the main risk element of the innovation and form the central part of the feasibility study.
Network Operability: The teed option will be confirmed in a policy update in line with Security and Quality of Supply Standard (SQSS) requirements. This PMS will offer a solution that provides network operability to disconnect the spur in the event of a fault in the same manner as that provided by a switching station. To allow disconnection and earthing of equipment, this will be provided via OHL jumpers and portable earths rather than fixed equipment. This will be reviewed and covered under a Hazard Review as part of the Feasibility.
Carbon: The PMS solution will firstly consider SF6 free options, but to ensure a full review other switchgear options may be considered as part of the feasibility.
As this project stage is limited to a feasibility assessment, at this time there is no requirement for a cost-benefit analysis as the technology readiness level (TRL) is 3. Although this technology has previously been deployed in North America, there is work to be done to ensure it is suitable for our network and to determine whether any adaptations are required. As part of the activities within the feasibility assessment, a full cost-benefit analysis will be completed and presented as part of the decision gate at the end of the project and will support the decision of whether to progress the project to stage 2, to carry out further development and testing or not.
Key Project Risks:
• To date and to our knowledge, this technology hasn’t been used in the UK – a key risk is that the technology has not currently been deployed outside of North America, although it has been used there for over forty years. The technology has been tested and proven in similar weather environments for decades however it has never been deployed by a UK Transmission Owner. To help mitigate this risk, the OEM has committed to providing continuous in-person support (if a contractual agreement is settled).
• Construction access – The project actively considers generator connections that are in remote areas. Getting the correct equipment to the site could be a risk for the project. As a mitigation, allowances for access roads will be factored into the cost estimate.
• Operational personnel not familiar with existing ground-mounted switches in an OHL arrangement or in using new OHL design plant and equipment. This will be mitigated by the activities carried out within this feasibility assessment.
• Ability to maintain protection and communications without the need to introduce ground-mounted infrastructure, batteries, and control panels. This will be mitigated by the activities carried out within this feasibility assessment.
